Method of chemically polishing copper and copper alloys



United States Patent M 3,345,225 METHOD OF CHEMICALLY POLISHING COPPER AND COPPER ALLOYS Rodolphe Lacal, Lyautey-Caen, France, assiguor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Aug. 31, 1964, Ser. No. 393,400 Claims priority, application France, Sept. 2, 1963,

3 Claims. (Cl. 15620) ABSTRACT OF THE DISCLOSURE A method of polishing copper in which the copper article is immersed successively in three baths, the first containing hydrochloric acid, hydrogen peroxide and glycerine, the second containing hydrogen peroxide and the third containing nitric acid. This abstract is not intended to. be a description of the invention defined by the claims.

The invention relates to a method of chemically polishing, more particularly polishing copper, by a simple immersion of the articles to be polished in three successive baths at the ambient temperature.

It frequently occurs, for several reasons, that copper articles have to be polished. For example, for reasons of outer appearance, a finish of the highest possible brilliancy and durability is aimed at. V

The polishing may also constitute a preparation for a later operation, for example, a weld or a deposit of another metal on the copper. In this case, the brilliant appearance given by the polishing permits of judging the quality of the polish necessary for a ready solderability or to obtain a deposit of the desired quality. It is known actually that, the appearance of articles covered with a deposit, the ease of the soldering, the resistance to corrosion depend upon the state of the surface of the metal of the base.

The polishing of the copper and copper alloys may be achieved by different methods. For example, .a mixture of acids may be used of which the composition varies within the following limits in accordance with the method to be treated:

The duration of the bath is from 2 to 6 minutes and the temperature from 55 to 80 C.

These baths have several drawbacks; their price is very high, they have a short duration of use due to their rapid saturation with metal; the control is diflicult; they give off nitric vapours and they must be kept at a certain temperature.

It therefore is necessary not only to degrease the articles beforehand, but also to de-oxidize or to pickle them. In general the results are poorly stable because the articles oxidize as soon as they come in contact with the air.

The invention avoids these drawbacks and has for its object to provide a method of chemically polishing copper and copper alloys consisting of immersing the article to be polished in three successive baths;

A first bath on the basis of HCl, H 0 glycerin, smooths the surfaces and forms a film on it which protects the Cu during the passage in air from the first to the second bath;

A second bath of H 0 which oxidizes the said film and renders the surface stable in air;

A third bath of HNO which dissolves the said oxidized film and produces the polish.

The treatments are carried out at the ambient temperature.

As to the first bath it is quite probable that its smoothing action is based on the preferred attack of the points that are projecting most where the decomposition of the hydrogen peroxide occurs in the easiest manner. On the other hand, the glycerin due to the viscosity which the hydroxyl group gives it, has two effects: it retards the reaction speed of the attack and forms on the elements to be polished a protecting layer which permits of performing the passage from the first to the second bath less rapidly without having to fear the action of the air.

In the second bath an oxidation of the film formed on the copper in the first bath is produced in a manner such that this film is soluble in the third bath.

This oxidation treatment of the second bath which modifies the absorbed layer is an important characteristic of the method according to the invention. In fact it has been found that if one passes immediately from the first bath to the third, the surface of the copper will be dull and unsuitable for being coated ultimately with metal.

The brown layer of oxide formed in the second bath is stable and is not modified by a stay in the air.

Therefore the method according to the invention avoids the above drawbacks and has the following advantages:

The copper need no longer be pickled, unless the superficial oxidation is excessive; when the amount of grease is important, the copper must be degreased but finger prints, for example, do not matter;

The activities are constantly carried out at the ambient temperature;

The bath is sufiiciently stable, and

The articles may be preserved after oxidation without the underlying surface being altered.

Consequently, they can be liberated from the oxidized layer only immediately before the metal deposit and, if desired, continuously that is to say in series. This is a great advantage, for the simple contact of the copper articles with the air is sufiicient to oxidize their surface and to give the metal deposits a bad quality, for example poorly adhering or hard to solder.

The articles obtained are particularly brilliant; their surface permits of a perfect solderability and an excellent quality of the metal deposits, notably those realised by displacement or reduction, which are very sensitive to their surface state.

The shine of these articles is particularly stable.

Another advantage is the possibility of varying the reaction speed in accordance with the article to be polished as may appear from the example of the method to be described below.

A particularly brilliant surface of copper is obtained by dipping the metal successively in the following solutions:

First bathhydrochloric acid (HCl), 6 N, 200 ml.; hydrogen peroxide (H 0 33.3% by weight, ml.; glycerin (CH OHCHOH-CH -OH) 50 ml.

Second bath-hydrogen peroxide (H 0 33.3% by weight.

Third bathnitric acid (HNO 0.25-0.5 N.

The elements to be polished are treated in the first bath for from 30 to 45 seconds and are then rapidly dipped in the second bath until a brown gold-plated colour is ob tained as uniformly as possible. Then these elements are dipped in the third bath until the polish appears.

It is interesting to add to the first bath a stabiliser of hydrogen peroxide which permits of augmenting its duration. A great number of stabilisers of this type are known: tartaric acid, acetic acid and, inter alia, the glycerin employed already in the bath for another reason. It is to be noted that this inhibiting effect of the glycerin on the decomposition of the hydrogen peroxide in hydrochlo- 3 ric medium is more accentuated in the presence of small quantities of NaCl.

It has been noted that the alteration of the layer on being contacted with the air avoids a ready polishing. Therefore the passage from the first to the second bath must be rapid. The presence of the glycerin, in this case also, has a favourable effect in that by diminishing the difiusion rate, the equilibrium of the layer which owing to the oxidizing medium must be formed from an unstable copper oxychloride, is fixed.

By varying, within certain limits, the concentrations of hydrochloric acid, glycerin, hydrogen peroxide and the time in the first bath, the same result may be obtained with a different reaction rate. In this manner it is possible to polish more easily a thin layer of copper (deposited notably electrolytically on another metal) without risking its complete dissolution which would take place for the concentrations indicated above.

An interesting variation has been realised with a composition of the first bath as follows:

HCl, 6 N, 200 mL; H 110 volumes, 100 ml.

The volume is brought to 600 ml. with a solution of E.D.T.A. (ethylene diamine tetra-acetic acid or a complex ion thereof) of 10 gr./1.

The advantage of E.D.T.A. is that it forms a complex with the copper during the reaction thus avoiding the decomposition of the hydrogen peroxide by the copper ions which augments the stability of the bath.

In addition, by adding to the first bath other acids (for example nitric acid, orthophosphoric acid) good results have been obtained, which may be interesting for certain copper alloys: these acids can attack the other components of the alloy.

In fact, thefirst bath may be modified according to the nature of the copper to be treated (thin layers, heating, etc.) in a manner such as to adapt the mixture to the thickness tolerance of the copper to be obtained while the final polishing succeeds all the same. With this end in View the concentration of the three products composing solution 1 may be varied. For example, if the hydrochloric concentration is diminished, the solution may give a favourable surface not only in the case of copper but also in the case of brass.

It is self-evident that several modifications may be applied without leaving the scope of this invention.

What is claimed is:

1. A method of chemically polishing an article essentially consisting of copper, said method comprising the steps, immersing said article in a first bath consisting essentially of hydrochloric acid, glycerine and hydrogen peroxide, immediately after withdrawal from said first bath immersing said article in a second bath consisting of a 33.3% by weight solution of hydrogen peroxide and then immersing said article in 0.250.5 N nitric acid.

2. A method of chemically polishing a copper article said method comprising the steps immerisng said article in a first bath consisting of 200 ml. of 6 N hydrochloric acid, 100 ml. of 33.3% by weight hydrogen peroxide and ml. of glycerine, immediately thereafter immersing said article in a second bath consisting of a 33.3% by weight solution hydrogen peroxide and then immersing said article in a third bath consisting of 025-05 N nitric acid.

3. A method of chemically polishing a copper article said method comprising the steps immersing said article in a first bath consisting of 200 ml. of 6 N hydrochloric acid, ml. of 33.3% by Weight hydrogen peroxide and a suflicient amount of a 10 gram per liter solution of ethylene diamine tetraacetic acid to bring the volume of said bath to 600 ml. immediately thereafter immersing said article in a second bath consisting of a 33.3% by Weight solution hydrogen peroxide and then immersing said article in a third bath consisting of 025-05 N nitric acid.

Metals Handbook, 1939 ed., pp. 1471 and 1472, Etching Copper, Davis.

JACOB H. STEINBERG, Primary Examiner. 

1. A METHOD OF CHEMICALLY POLISHING AN ARTICLE ESSENTIALLY CONSISTING OF COPPER, SAID METHOD COMPRISING THE STEPS, IMMERSING SAID ARTICLE IN A FIRST BATH CONSISTING ESSENTIALLY OF HYDROCHLORIC ACID, GLYCERINE AND HYDROGEN PEROXIDE, IMMEDIATELY AFTER WITHDRAWAL FROM SAID FIRST BATH IMMERSING SAID ARTICLE IN A SECOND BATH CONSISTING OF A 33.3% BY WEIGHT SOLUTION OF HYDROGEN PEROXIDE AND THEN IMMERSING SAID ARTICLE IN 0.25-0.5 N NITRIC ACID. 